Electrical power system



1954 A. v. JOHANSSON ETAL 2,697,199

ELECTRICAL POWER SYSTEM Filed April 18, 1952 n Y. o, e

s w ome .t t m A J .m in Qmfl 0 United States Patent 2,697,199 ELECTRICAL POWER SYSTEM T. Means, Erie, Pa., General Electric Company, a corporation August V. Johansson and Thomas assi' nors to of New York Application April 18, 1952, Serial No. 282,972 13 Claims. (Cl. 322-27) This invenution relates to electrical power systems and more particularly to prime mover driven electrical power systems for self-propelled vehicles.

In the design of self-propelled vehicles, such as dieselelectric locomotives, it may b previously been designed with control a plurality, for example, eight increments of tractive effort for starting and operating trains.

of measuring the actual current produced by the gensiderable period of time, these currents may exceed the short time ratings of the traction motors. These currents are obtained in throttle notches so low that the traction motor blowers, which operate at a speed proportional to locomotive, since, due controlling motor current at the same value on several coupled units, the current on such trailing units may 2,697,199 Patented Dec. 14, 1954 It is, therefore, seen that a tive effort control a multiple unit locomotive. A n object of this invention is,

order to maintain the generator line current at the pre- More specifically, such an arrangement may be a magnetic amplifier having a rectified output connected to vary the voltage applied to th separately excited field of the generator with one direct current winding being energized from the resistance bank in across a series field winding,

' the generator so that the magnetic of the prime mover. Thus, a plurality of predetermined prime mover speeds and an equal number of predetermined generator excitation levels are provided by the controller.

In order to provide s control amplidyne exciter controller 45.

the maximum value of. the control voltage down to a lower level. Thus, in each notch of the main controller, the tractive effort may be reduced from the maximum level of that particular notch down to a by manipulation of the movable tap of the potentiometer. In order to provide for multiple unit operation, a train wire circuit is provided in each locomotive unit adapted to be connected to a similar train wire circuit in each o her vehicle. The movable tap of the notchless tractive efiort potentiomeer is connected to the train wire with the resistance bank in each vehicle being selectively connected either directly to the source of control voltage or to the train wire. Thus, manipulation of the notchless tractive effort potentiometer in lead locomotive unit will vary the voltage on the train wire in each unit thus applying the same volta e to the resistance in each unit and therefore providing the same generator excitation in each unit.

The single figure of trates the improved electrical power system of invention.

Referring now to the drawing, there is shown a traction generator 1, having a separa ely excited field exciting winding 2 and a series field excitin winding 3, for example a commutating pole winding. The enerator 1 is adapted to be connected to a lurality of tracti n mot rs, one bein shown schematic ll at 4. t will be readily unders od that suitable s itching arrangements would be provided to connect he traction motors 4 for either series or parallel operation. however, since these arrangemen s form no part f this invention, they will not be further described. The separately excited field exciting winding 2 of the generator 1 is connected for energization from an exciter machine Shaving a control field exciting windin '6. The exci er machine 5 may be an armature reac ion excited m chi e of the type referred to as an amplidy e. Both the e erator 1 and the exciter machine 5 are driven by a suitable prime mover 7, such as a diesel engine.

In order to energize the contr l fie d wind n 6 of the 5, the control field windin is cona source of contr l voltage 8 and 9 and has a resistor 1.0 arranged in series th rewith. In order to vary the voltage appearing across the amplidyne c ntrol field winding 6 and thus vary the e citati n supplied to the genera r se arately exc ed field winding 2. a magnetic amplifier 11 is provided h in a pair of threelegged core reactors 12 and 13. The outer legs of the reactors 12 and 13 are r vided with windings 14, 15, 16 and 17 which are serially connected for ener ization from a suitable source of alternating current (not shown) by lines 18 and 19. A brid e rectifier 20 has its input connected across line 19 and the connection between alternating current windin s and 16 as at 21. The output of the bridge rectifier 20 is connected across a resistor 10 in series with the amplidyne exciter control field winding 6. In order to control magnetic amplifier 11, a pair of direct current windings 22 and 23 are respectively arranged on the center'legs of the reactors 12 and 13 and serially connected across the source of control voltage 8 and 9. Another direct currentwinding 24 is arranged on the center .leg of reactor 12 and connected across series field exciting winding 3 of generator 1. Windings 22 and 24 on reactor 12 are arranged to be additive.

In order to control the input to the magnetic amplifier 20 and ultimately the excitation applied to the separtely excited field exciting winding 2 of generator 1, a resistance bank 25 is provided having taps 26 through 32 inclusive. The resistance bank 25 has its end 26 connected to positive control line 8 through normally closed contact 34 of hump control relay 35 with fixed resistance 36 being arranged in the circuit. The taps 26 to 32 of resistance bank 25 are respectively connected to cam actuated contacts the drawing schematically illusthis nected across 43 being also connected to common line 46. Common line 46 isin turn connected to the negative control line 9 through contact 44 of drum The direct current winding 23 of reactor 13 is connected across the resistance bank 25 by means of line 47 connecting the end 26 of resistance bank- 25 and the connection 48between direct current windings 22 and 23'; and cornmon'line '46 to which reactor coil 23 is connected at 49. The drurn controller-AS has eight positions and an off position, the contacts 37 to much lower value 37 through 43 of drum controller 45, the contacts 37 to across direct current reactor appearing across point 21 and line bridge rectifier 43 being successively closed in the first seven positions to progressively short sections of the resistance bank 25 and none of the contacts 37 to 43 being closed in the eighth position. The contact 44 connecting common line 46 to the negative control line 9 is closed in each of the eight positions of controller 45 and open in the oil position.

Assuming for the moment that voltages appearing windings 22 and 23 are equal so that equal saturation is provided in the cores 12 and 13, it will be seen that the voltage appearing across point 21 and line 19 will be equal to the voltage 13 and therefore half of the voltage appearing across lines 18 and 19 will be impressed upon the bridge rectifier 20 and the rectified output applied to the resistor 10. The voltage impressed by the rectifier 20 on the resistor 10 is arranged to buck the voltage across control lines 3 and 9 and thus the ultimate voltage appearing across amplidyne exciter control field winding 6 will be the difference between the control voltage appearing across lines 8 and 9 and the bucking voltage impressed upon the resistor 10 by the 29. Assuming now that generator 1 is connected to traction motors 4 so that load current flows of reactor 12 and through windin s 14 and 15 peering through the series field exciting winding 3, a voltage will appear across the direct current winding 24. This will increase the unidirectional flux flowing in the center leg the side legs on which the are Wound and the resultant increase in saturation of reactor 12 and in the reactance of windings 14 and 15 will therefore decrease the voltage appearing across point 21 and line 18. The voltage apacross point '21 and 'line 19 will therefore increase by a corresponding amount thus increasing the voltage impressed upon the bridge rectifier 2t) and the bucking voltage applied to the resistor 10. With an increase in the bucking voltage, the voltage across the amplidyne exciter control field winding 6 will be decreased by a corresponding amount, thus decreasing the excitation applied to the generator separately excited field winding 2 and decreasing the line current supplied by generator 1. Correspondingly, a decrease in the line current flowing in the series field winding 3 of generator 1 will decrease the voltage appearing across direct current winding 24 of reactor 12 thus decreasing the unidirectional fiux producing a corresponding decrease in reactance of windings 14 and 15. This will increase the voltage appearing across point 21 and line 18 with a corresponding decrease in the voltage across point 21 and line 19. This in turn produces a decrease in the voltage applied to the bridge rectifier 2t and the voltage impressed upon resistor 10 so that increased voltages are applied to amplidyne exciter control field winding 6 and to generator separately excited field winding 2. Thus, an increase in the generator line current will be produced. It is thus seen that with the voltages appearing across direct current windings 22 and 23 remaining constant, an increase in line current flowing in the field winding 3 will produce a corresponding decrease in the excitation supplied to separately excited field winding 2 to restore the line current to its original value and correspondingly a decrease in the line current flowing in the field winding 3 will produce a corresponding increase in the excitation applied to the separately excited field winding 2 to again restore the current to its original level. Thus, the line current of the generator 1 is measured in order to vary the excitation supplied to the generator 1 tomaintain the line current at the desired level.

It will now be readily seen that varying the amount of resistance across direct current winding 23 by operating controller 45 to progressively close contacts 37 to 43 and thus progressively short the sections of the resistance bank, will increase the voltage applied to the winding 23 and decrease the voltage applied to the winding 22. Thus, assuming that controller 45 is in the first position with contact 37 closed, the entire resistance bank 25 and thus the winding 23 will be shorted and the entire voltage across control lines 8 and 9 will appear across winding 22. With this condition, the reactor 12 will be highly saturated so thata low voltage appears across point 21 and line 18 with variations in, he voltage applied to winding 24 varying the voltage about that level. Thus, the voltage across point 21 and line 19 and thus across rectivoltage applied to winding 24 responsive to generator-line 2,697,199 current producing variations in the rectifier output about moved toward its other extremity 64 to continuously that level. It is therefore seen that with resistance bank reduce the voltage applied to the circuit including the 2: completely shorted, a high level of bucking voltage fixed resistor 36 and the resistance bank 25. It is thus as applied to resistor 130 by rectifier 20 and thus a relaseen that as the controller 54 is advanced the voltage tively low level of excitation is supplied to amplidyne ex- 5 across that portion of resistance bank 25 selected by citer control field winding 6 and generator field winding controller 45 is reduced thus reducing the voltage on the owever, as contacts 37 to 43 of controller 45 are reactor winding 23 This 111 turn increases the input to progressively closed as the controller is moved from bri ge rectifier 20 thus increasing the bucking voltage "position 1 to position 7, it is seen that progressively applied to the resistor 10 and decreasing the voltage on the larger sections of resistance bank 25 are connected across 10 amplidyne exciter control field winding 6. Thus, as the of controller 45, none of the resistance bank 25 is conby to reduce the generator line current called for.

nected across direct current winding 23 so that the high- Since the train wire 55 is connected to similar wires est voltage appears thereacross reducing the voltage apin other locomotive cabs and since the same control plied to rectifier and thus to the bucking resistor 10 arrangement is found in each cab it will be apparent to the lowest level. The voltage therefore applied to that by manipulating controller 54 in the lead cab the amplidyne exciter control field Winding 6 is at its highest voltage on the train wire is varied in each cab thus prolevel to call for the highest current output of generator 1. 20 ducing the same variation in the voltage appearing across t is t us seen that the generator current is varied in a resistance bank and resistance 36 and in the excitaplurality of steps, shown here as being 8, by manipulation supplied to the generator in each cab The controller tion of drum controller 45 and that in each position of the 7 is connected in the circuit since it might otherwise Controller 45 calling for a predetel'fnlned level of g abe possible for someone to manipulate potentiometer 51 tor hhe Current the magnetle p 11 energlled f 25 in one of the trailing cabs and thus adversely affect the P e Current flowing in generator Series field Windtractive effort called for by the engineman. To elimi- 3 W111 modify e bucking voltage appearing across nate this possibility, it will be noted that in each of the resistor 10 to maintain the current at the desire leveltrailing cabs, the resistance bank 25 and resistance 36 are t W111 he y nnderstnod that In mulhple unit P supplied directly from train wire 55 through contact 62.

tlOn, the System thus far described Will he Provided in Since the handle for controller 57 will only be found in e cab i h the eohtholler Shown schematically at 45 the lead cab, and thus the contacts 56 in the trailing each traihng cab being Operated y h englpeman units will not be closed, it will be impossible for anyone 1n the leadlng Thls System of multlple unit to operate the potentiometer 51 in any of the trailing trol does not form a part of this invention and will not be cabs to change h ti c ll d f r by the enginei'nan more fully described. Hump control relay has a normally open contact 65 It W111 be 'e y Seenthat Wlth the arrangement hereln which shorts switch 52 thus permitting the controller 54 effort of the locomotive can to be returned to the off or full field position 63 without It will be seen that this system provides a gradually 40 increasing range to the total movement of the hump control potentiometer 51 as the controller is advanced toward the higher notches. For example, in notch 1 of controller 45, the minimum engine speed is called for by virtue of the connection of the controller45 to the mg arranged in series therewith. The movable tap 53 of hump control potentiomter 51 and switch 52 are both operated by hump controller 54 with tap 53 being con- 45 nected to train wire 55 through contact 56 of reverser orator excitation is called for since the resistor bank 25 contronfir and i It W111 be readlly undqstciod is completely short-circuited. In this notch, no control t train i 55 13 adapted. to to slmllar is provided by hump control potentiometer 51 since the train wires in other locomotive units and that the cong g g gg g g gg gg ggg xg z ggg sh established by reactor winding 22 which in the first notch di ectl ener ized across lines 8 and reverse positions with contact 56 being closed in the of controller 4518 X g ni ulation of the hump control potentiometer 51 will 32 32 3 f g i g: g s gg fi g co htinuously vary the tractive effort downward from that con being connected to common lme 46 e 0mm called for by the particular controller notch to a much ating coil 59 of hump control relay 35 is also arranged to kwer g fi gi giggg jggg g g gg sfif ig f be connected directly to ositive control line 8 through its 60 g i t 1 t t 51 t p t normally open contact 61. It will thus be seen that with 6 Wu ump Con m p0 lome er 1 5 ex reml y the movabia tap 53 0 mm) control potentiometer 51 64 since in this position resistor 36 is eite tively conin the position shown in the drawing so that switch 52 is meted parallel Wlth resistance i Wlth h closed with the reverser 57 in either the forward or the Work a parallel connected h wmdmg bemg fed reverse position so that the contact 56 is closed, operat- 65 from lme 8 through reactor Winding It W111 be seen ing coil 59 of control relay 35 will 6 energized that once the hump control switch 5215 closed the hump mm line 3 and will pick up thus Opening its normally control relay 35 will pick up sealing itself into the closed contacts 60 and sealing itself in directly to line 8 posmYe i hne 8 throuolil Its fi through its contact 61. Picking up of hump control relay ever It will sfaen t .When t 6 Contra er i moved 35 opens its normally closed contact 34 which connected to or 'dhng q contaq 44 copnectmg resistance bank 25 and resistance 36 to positive control moh hhe 46 to hegahve control hhe 9 W111 he Opened line 8 and closes normally open contact 62 connecting ret us opehlhg the clrchlt 0f opelatlhg c011 59 0f mp sistance bank 25 and fixed resistor 36 to the train wire 55. chhtrol relay to drop out the relay Capacltor 67 P t is now seen that resistance bank 25 an resistance 36 Vldes a temporary P for the P p current of relay are energized from positive control line 8 through switch 5 35 durlng the Instant when Contact 50 1S p and 52, potentiometer 51, contact 56, line 58. train wire 55, o c0ntact61 hasclosed. v and contact 62. It is thus seen that with the movable tap To s mmarize, it will now be readily seen that the 53 f hump control potentiometer 51 at h extreme d excitation supplied to generator 1 and thus the line cur- 63 as shown in the drawing, the volta e applied to the n of the generator 18 Set at a P V p q resistance bank 25 and resistance 36 will be the same as Inlned Values y means f the n ll 45 hlCh lmu1- that applied when the resistance bank and fixed resisttaneouslysets the speed of the diesel 7 at a plurality of ance are connected directly to the positive control line 8 pre rmin lu Th in r n f t generator through contact 34 of hump control relay 35. However, 1' is measured by means of the reactor coil 24 and the it will be seen that by operating hump -controlier'54, the magnetic amplifier 11 functions to-maintain the line curmovable tap 53 of hump control potentiometer 51may be rent at the desired predetermined value, the amount of aee znae the resistance bank: 25. connected in :parallelwith; reactor winding 23'determiningthe1 generator line current level.. In order to providethe notchless tractive. effort humping:

control, the train wire 55 and all similar train wires in other cabs, are energized to pick up the hump control relay 35, energizationof trainwire 55 in-other locomotive cabs also picking upthe hump control relays in those cabs through lines 58. Picking up of the hump control relays 35 connects resistance ban to the train wire SSrather than directly to the positive control line 8, the train wire 55' being in turn energized from the movable element 53 of hump control potentiometer 51. It is thus seen that this invention requires. the use of only one train wireforinitially setting up the notchless hump control system and for subsequent modulation of the control in both the leading cab and trailing, multiple. unit cabs. notchless tractive effort, control without danger of over,- load of the traction motors of any one of a group ofmultipleunit connected cabs since each of the locomotive units is provided with the generator current limiting arrangement here shown. In addition, this arrangement can be readily added to existing locomotives having an eightnotch throttle and a current limit excitation. system. Itis, therefore, vides an improved electrical propelledvehicle characterized by its simplicity, installation, and superior tractive effort control.

While we have shown and described a particular embodiment of this invention, further modifications an improvements will occur to those skilled in the art. We desire it to be understood, therefore, that this invention is. not limited to the form shown and we intend in the appended claims to cover all modifications which do not depart from the spirit andscope of this invention.

What we claim as new and desire to secure by- Letters Patent of the United States is:

1. An electric power system for a self-propelled vehicle comprising a generator having exciting means, a source of control voltage, a resistance bank having a plurality of power system for a selfeaseaof sections, supervisory control means having a plurality of positions arranged selectively to connect said resistance sections in circuit with said exciting means thereby to vary the excitation supplied to said generator in a plurality of steps, a continuously variable potentiometer connected across said source of control power and having a movable tap, a train wire circuit adapted to be connected to similar circuits in other vehicles, said movable tap of said potentiometer being connected to said train wire circuit, switch means arranged selectively to connect said resistance bank directly to said source of control voltage or to said train wire circuit thereby smoothly to vary the voltage applied to said resistance bank whereby the excitation supplied to said generator is smoothly varied, and other supervisory control means arranged to operate said potentiometer tap.

2. An electrical power system for a self-propelled vehicle comprising a generator having exciting means, a source of control voltage, a resistance bank having a plurality of sections, supervisory control means having a plurality of positions, arranged selectively to connect said resistance sections in circuit with said exciting means thereby to vary the excitation supplied to said generator in a plurality of steps, a train wire adapted to be connected to similar circuits in other vehicles, a continuously variable potentiometer connected acrosssaid source of control voltage and having a movable tap connected a relay having an operating to said train wire circuit, coil with one side thereof connected to one side of said source of control voltage and having its other side con-- nected to said train wire circuit, said relay having a contact connecting said resistance bank directly to said control voltage when said relay is deenergized and another contact connecting said resistance bank to said train wire circuit when said relay is energized so that operation said potentiometer smoothly varies: the voltage applied to said resistance bank thereby smoothly to vary the excitation supplied to said generator, andother supervisory control means arranged to operate said potentiometer tap,

3. An electrical power system for' a self-propelled vehicle comprising a generator havingan excitingmeans, a source of control voltage, a resistance hank. having a plurality of. sections;. supervisorycontrol..meansihavin a pluralityofpositions arrangedsele'ctively toecnnect said k 25 and resistor 36' Furthermore, this system. provides.

readily apparent that this invention prosaid= resistance aloadandhaving a separately exclted ing, a'source of voltage rality of sections, supervisory control resistance sectionszincircuit.withsaidexciting means therebyto vary the excitation supplied to said generator in a plurality of steps, a trainwire circuit adapted to be connected to similar circuits and other vehicles, a continuouslyvariable potentiometer connected across said source of control voltage and having a movable tap connected to said train wire circuit, a relay having an operating coil with one side thereof connected to one side of said source of control voltage, said relay having a contact connecting the other side of said operating coil to said train wire circuit'when said relay is deenergized and another contact connecting said other side of said other side of said source of control voltage when said relay is energized, said relay having a contact connecting bank directly to said source of control voltage when said relay is deenergized and another contact connecting said resistance bank to said train wire circuit-when. said relay is energized whereby said potentiometer smoothly varies the voltage applied to said resistance bank thereby smoothly to vary the excitation supplied to said generator, and other supervisory control means arrangedto operate said potentiometer tap.

4. An electrical power system for a self-propelled vehicle comprising a generator adapted to be connected to field exciting windfor energizing said separately excitedfield winding, a magnetic amplifier having a rectified-output connected to vary said voltage thereby to vary the excitation supplied to said separately excited field winding, said magnetic amplifier having a direct current winding electrically connected for energization responsive to the load current of saidgenerator whereby the excitation supplied to said separately excited field winding is varied thereby to maintain said generator load current at a predetermined value, said magnetic amplifier having another directcurrent winding, a resistance bank having a plurality of sections, supervisory control means having a plurality of positions arranged selectively to connect said resistance sections to said other magnetic amplifierdirect current winding thereby further to vary the energization supplied to said separately excited field winding whereby the value of said generator load current is established, a source of control voltage, means arranged smoothly to vary said source of control voltage, switch means arranged selectively to connect said resistance bank directly to said source of controlvoltage or to said continuously varying means thereby smoothly to vary thevoltage'applied to said resistance bank whereby the excitation supplied to said generator is smoothly varied, and other supervisory control means arranged to operate said continuously variable means.

5; An electrical power system for a self-propelled vehicle comprisinga generator adapted to be connected to a load and having a separately excited field exciting winding, a source of voltage for energizing said separately excited field winding, a magnetic amplifier having a rectified output connected to vary said voltage thereby to vary the excitation supplied to said separately excited field windings, said magnetic amplifier having a direct current winding electrically connected for energization responsive to the load current'of said generator whereby the excitation suppliedto said separately excited field winding is varied thereby to maintain said generator load current at a predetermined value, said magnetic amplifier having another direct current winding, a resistance bank having a plumeans having a plurality of positionsarrangedselectively to connect said resistance sections to said other magnetic amplifier direct current winding thereby further to vary the energization supplied to said separately excited field winding whereby the value of said generator load current is established, a source of control voltage, a continuously variable potentiometer connected across said source of control voltage and having a movable tap, switch means arranged selectively to connect said resistance bank directly to said source of control voltage or to said potentiometer tap thereby smoothly to vary the voltage applied to said resistance bank. whereby the excitation'supplied to said generator issmoothly varied, and other supervisory control means arranged to operate said potentiometer tap.

6. An electrical power. system for a self-propelled vehicle comprising 'a: generator adapted .to be connected to a load. and having aseparatelyexcited field exciting winding-, a source" ot'1v0ltagefor energizing said separately excitedlfield winding, amagnetic amplifier. having ax reetifiedioutput connected-.to-varysaid voltage thereby operating coil to sa d .field winding, said to vary the excitation supplied to said separately excited magnetic amplifier having a direct current winding electrically connected for energization responsive to the load current of said generator whereby the QXCH atlOIh supplied to said current at a predetermined value, said magnetic amplihaving another direct current wlndmg, a resistance switc means arranged selectively to connect said resistance bank directly to said source of control voltage or to said train Wire circuit thereby smoothly to vary the smoothly varied, and other supervisory control means arranged to operate said potentiometer ta a source of voltage for energizing said separately excited a magnetic amplifier having a rectified output connected to vary said voltage thereby to vary the having a plurality of sections, superv1sory control means having a voltage, ranged selectively to connect said resistance bank directly to said source of control voltage or to said continuously varying means thereby smoothly to vary volt age applied to said resistance ank whereby the excitation supplied to said generator other supervisory control means arranged to vary said continuously varying means.

I0 9. An electrical power system for a self-propelled ve hicle comprising a generator adapted to be a load and having a separatcfy excited field exciting winding, a source of voltage for energizing said separately excited field winding, means ing a movable tap, switch means arranged selectively to connect said resistance bank directly to said source of or to said potentiometer tap thereby smoothly to vary the voltage applied to said resstance smoothly varied, and other arranged to operate said potentiometer 10. An electrical power system for a self-propelled vehicle comprising a generator adapted to be connected to a load and having a separately excited field exciting winding, a source of voltage for energizing said separately excited field winding, means for varying said source of eter tap.

12. An electrical power system for a self-propelled ve hicle comprising a generator adapted to be electricallyconnected to a load and having a separately excited field exciting winding, a source of voltage connected to energize said eluding a magnetic amplifier having a rectified output 11 rentwindings serially connected across source of control voltage, a resistance circuit including a resistance bank having a plurality of sections arid another resistance connected in series therewith, a train wire circuit adapted to be connected to similar circuits in other vehicles, supervisory control means having a plurality of positions arranged selectively to connect said resistance bank sections to'one of said magnetic amplifier direct current windings thereby to vary the voltage'supplied to said one magnetic amplifier direct current winding whereby the'excitation supplied to said separately excited field winding is varied to determine the load current of said generator, said magnetic amplifier having another direct current winding energized responsive to the load current of said generator whereby said load current is maintained at the value determined by said supervisory control means, a continuously variable potentiometer connected across said source of control voltage and having a movable tap connected to said train wire circuit, switch means arranged selectively to connect said resistance circuit directly to said source of control voltage or to said train wire circuit whereby said potentiometer smoothly varies the voltage applied to said first-named circuit thereby smoothly to vary the excitation supplied to said generator,

and othersupervisory control means arranged to operate said potentiometer tap.

13. An electrical power system for a 'self propelled vehicle comprising a generator adapted to be electrically connected to a traction motor and having a separately excited field exciting winding and winding, a source of voltage connected to energize said separately excited field winding, means including a magnetic amplifier having'rectified-output connected to vary said voltage thereby to vary the excitation supplied to said separately excited field winding, plifier having a pair of direct current windings serially connected across said source of control voltage, a resistance circuit including a resistance bank having a plua series field exciting said magnetic am-' the load current of said generator rality'of sections 'and another resistance connectedin' series therewith, a train wire circuit adapted to be connected to similar circuits-in other vehicles, supervisory control means having a plurality of positions arrange selectively to connect said resistance bank sections to one of said magnetic amplifier direct current windings thereby to vary the voltage supplied to said one magnetic amplifier direct current winding whereby the excitation supplied to said separately excited field winding is varied to determine the load current of said generator,

said magnetic amplifier having another direct current Winding connected across said series field winding Whereby said first-mentioned voltage is varied responsive to thereby to maintain said load current at the value determined by said supervisory control means, a continuously variable potentiometer connected'across said source of control voltage and having a movable tap connected to said train wire circuit, a relay having an operating coil with one side thereof connected to said source of control voltage and the other side to said train wire circuit, said relay having a contact connecting said resistance circuit directly to said source of 'control'voltage when said relay is deenergized 'and'another contact connecting said resistance circuit to said train wire circuit when said relay is energized whereby said potentiometer smoothly varies the voltage applied to sai resistance circuit thereby smoothly to vary the excitation supplied to said generator, and other supervisory controlmeans arranged to operate said potentiometer tap.

References Cited in the file of this patent UNITED STATES PATENTS 

